The electronic whiteboard system adopting optical imaging technology is realized through optical pen position tracking, see the China patent of the “System and Method for Computer Information Input Coordinate & Control” with the patent No. ZL011080477 and patent publication No. CN1305143A for detailed information. The operating principle: the target positions are marked by light spots generated by the optical pen, and a photographic device is adopted to collect images in real time. The signal processing circuit is used to analyze image signals in real time and extract the position information of the light spots, which is input into the computer through the interface circuit and the relative software. The coordinate correction algorithm is applied to perform calibration so that the position of the cursor can track the physical position of the optical pen. The current technology generally introduces an optical band-pass filter to ensure the best utilization of spectral energy and the best filtration of ambient light energy for the sake of high signal-noise-ratio (SNR) and operation stability, or increases the SNR by amplifying the light-emitting power. However there is a limit in the effect of using filters since light disturbance is still liable to occur under a certain luminance of the optical pen with possible strong ambient light and in addition, if the light-emitting power is increased too much, the power consumption will be high and the battery will be quickly drained. So a better method for further increasing the SNR should be developed.